Letter to the Editor

NGC 5506 unmasked as a Narrow Line Seyfert 1:^*

A direct view of the broad line region using near-IR spectroscopy

¹ INAF, Arcetri Observatory, Largo E. Fermi 5, Florence 50125, Italy
² INAF, Telescopio Nazionale Galileo, Aptdo de Correos, 565, 38700 Santa Cruz de La Palma, Canary Islands, Spain

Corresponding author: N. Nagar, neil@arcetri.astro.it

Received: 12 May 2002
Accepted: 13 July 2002

Abstract

This letter presents incontrovertible evidence that NGC 5506 is a Narrow Line Seyfert 1 (NLSy1). Our new 0.9–1.4 μm spectrum of its nucleus clearly shows the permitted m line (with full width at half maximum <2000 km s^-1) and the “1 micron  lines”. These lines can only originate in the optically-thick broad line region (BLR) and, among Seyfert nuclei the latter series of lines are seen only in NLSy1s. The obscuration to the BLR, derived from a rough estimate of the m/ 8446 ratio and from the reddening of the near-IR Paschen lines, is . Together, these results make NGC 5506 the first identified case of an optically-obscured NLSy1. This new classification helps explain its radio to X-ray properties, which until now were considered highly anomalous. However, interesting new concerns are raised: e.g., NGC 5506 is unusual in hosting both a “type 1” AGN and a nuclear water vapor megamaser. As the brightest known NLSy1, NGC 5506 is highly suitable for study at wavebands less affected by obscuration.